Blog Post Categories
Adding Tags to a post Categorizes that post on your sidebar. Categorizing a post in this way allows visitors to your blog to easily find posts that cover a specific topic.
Tagging a Post is as easy as using the Category section to check off any previously added Categories that apply and adding any new Category that seem appropriate.
The Categories can be found in the Post Options section.
To add a Category, click on the Add Categories button.
Once you add a Tag it's always available to use for future posts.
Any Categories that are tagged in the blog posts will show up in the Categories section of your blog's sidebar. Clicking on a category will display all blog posts that were tagged with that Category.
If you don't see a Categories section on your sidebar, you can add one by dragging a Categories element to the page.
Keep in mind you should limit the number of Categories or 'Tags'. If you keep the number of Categories to a minimum (say, less than twenty or so) it'll be easier for visitors to find posts that interest them. Creating a new Tag for almost every post makes the Categories difficult to navigate and significantly less useful for your visitors.